MySQL Creating a Function with conditional

Question

I am trying to create a mysql function with a condition that I certain word must be in the parameter for it to work

CREATE FUNCTION hello (s CHAR(20)) RETURNS CHAR(50) 
DETERMINISTIC 
IF s = NULL 
THEN RETURN CONCAT('Hello World!')

So if the query is

SELECT hello(NULL);

Then it should output:

+--------------------+
| hello(NULL)        |
+--------------------+
| Hello Hello World! |
+--------------------+

Otherwise there shouldn't be any rows returned

When I try to do my code above, it always return a syntax error. The thing is I 'm not really good at creating mysql functions especially if there are conditionals

PS

I tried this code but I got the following error

mysql> CREATE FUNCTION hello (s CHAR(20)) RETURNS CHAR(50) 
    -> DETERMINISTIC 
    -> IF s IS NULL 
    -> THEN RETURN CONCAT('Hello World!');
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 4

Answer 1

Your function has several syntax errors:

 DELIMITER &&

 CREATE FUNCTION hello (s CHAR(20)) RETURNS CHAR(50) 
 DETERMINISTIC 
 BEGIN
     IF s IS NULL THEN
         RETURN CONCAT('Hello World!');
     END IF;
 END&&

 DELIMITER ;

• Try to define a delimiter
• Use begin, end in function body
• You need end if for if clause
• = null should be is null

Answer 2

You need to use IS NULL or IS NOT NULL, not the equal sign. So change your query to:

IF s IS NULL 
THEN RETURN CONCAT('Hello World!')

Please check the answer in this stackoverflow question which explains this topic.